Chromium oxide catalyst



Patented Jan, 18, 1944 UNITED STATES PATENT FFICET- CHROMIUM OXIDE CATALYST Glen H. Morey, Terre Haute, Ind., assignor to Phillips Petroleum Company, a corporation of Delaware Serial No. 359,295

No Drawing. Application October 1, 1940,

12 Claims; (01. 252-251) This invention relates to the preparation of chromium oxide catalysts, and more particularly to the preparation of catalysts comprising dark -or black unglowed chromium oxide. This applito the corresponding monoolefins, the dehydrogenation of paraflins or monoolefins to the corresponding diolefins or acetylenes, or the formation of cycloolefins, cyclodiolefins or aromatic hydrocarbons from aliphatic or naphthene hydrocarbons; or the change'may be effected by hydrogenation, as, for example, in the nondestructive hydrogenation of diisobutylene to isooctane and in the nondestructive hydrogenation of unsaturated polyme'r gasoline into motor fuel of less, unsaturated characteristics. In certain iiistances, such changes in the carbon-to-hydrogen ratio may be accompanied by isomerization-type reactions, such as those involved in the reforming and/or cyclization of some hydrocarbons boiling in the motor-fuel range, such as in the conversion of hexane to benzene, heptane to toluene, etc. The catalysts are also useful for other treat-' ments of hydrocarbon fractions or mixtures, such --as desulfurization of sulfur-containing gasolines.

A chromiumi oxide gel catalyst suitable for efiecting changes in the carbon-to-hydrogen ratios of hydrocarbon has been described in. U. S. Patent No. 1,905,383, and in an article published by Frey and Huppke in Industrial and Engineering Chemistry, vol. 25, January, 1933, pp. 54-59. U. 8. Patents Nos. 2,098,959 and 2,098,960 disclose the incorporation or homogeneous commingling, with the chromium oxide of'one or more diflicultly reducible oxides, such as alumina, zirconia,

' thoria, silica, magnesia, titania, boric oxide, or

the like, in such a way'that the gel characteristies are conserved, as by coprecipitation or by intimate intermixing of the freshly precipitated hydrous oxides; incorporation of readily reduci bleheavy-metal oxides, such as those of thallium, bismuth, lead, and mercury, is also disclosed. In

the preparation of these catalysts, which contain unglowed chromium oxide, 9. solution containing a chromic salt is used, and dark-green gelatinous hydrated chromium oxide is formed by precipitation with an alkali solution, such as a solution of ammonia, sodium hydroxide, potassium hydroxide, or the like. The hydrous material com-.

prising the green gelatinous hydrated chromium oxide is suitably washed and dried; the resulting homogeneous oxide mixture is broken into granules of a suitable size, and it is suitably reduced in an atmosphere of a reducing gas before being used as a catalyst.

The copending application of Morey and Frey, Serial No. 173,709, filed November 9, 1937, which has issued as Patent No. 2,312,572, discloses that the drying of the hydrous gel is advantageously controlled in such a way that the gel contains, immediately before the reducing tep, chromium with a valence of more than three, but at least in part probably less than six, to an extent equivalent to a hexavalent-chromium content of 1 to 40 per cent, preferably 15 to 35 per cent, of the total chromium. The desired content of highervalent chromium is preferably obtained by drying the hydrous material in an oxidizing atmosphere, such as air, at a temperature gradually increasingfrom room temperature to a temperature within the range of about 300 to 400 F.

The last-mentioned copending application (Patent No. 2,312,572) also discloses that the reducing step is advantageously conducted in a reducing atmosphere under such conditions that the temperature of the chromium oxide rises slowly within the range of about 300 to 570 F. and that reduction of chromium with a valence higher than three is effected without spontaneous thermal decomposition of more than a negligible proportion of chromium oxide having such higher-valent chromium. Simultaneously, the gel is dehydrated beyond the state reached in the preceding drying in an oxidizing atmosphere. Still further dehydration is effected by a. raising of the temperature, after the reduction is complete, above 570 F.; the dehydration is substantially complete if the temperature is raised to a value within the range preferred for the dehydrogenation of hydrocarbons, namely, about 750 to When a catalyst containing unglowed chromium oxide is used for the conversion of hydrocarbons by changingthe carbon-to-hydrogen ratios thereof, it is maintained at an elevated tem-; perature, generally within the range of 390 to olefin, but more than especially solutions 1100' tiv'ely most useful in F. The lower part or this range is relathe hydrogenation of unsaturated hydrocarbons, and the upper part in the dehydrogenation of hydrocarbons; The pressure and the time of contact may be varied over wide ranges, in accordance with the requirements of the particular conversion in hand. For example, the pressure may be atmospheric; or, it may be superatmospheric, which is advantageous for hydrogenation; or it may be subatmospheric, which is advantageous for dehydrogenation, although, of course, slight superatmospheric pressures are generally used even in dehydrogenation processes, in order to eration. Similarly, for a particular temperature, a contact time of a fraction of a second to several seconds may be adequate for dehydrogena the corresponding monoseveral seconds may be necessary to effect further dehydrogenation or cyclization. In any particular case, suitable conditiorm of use may be readily found by trial. The catalysts may be repeatedly revivified by buming off carbonaceous or other matter, deposited thereon during use, with an oxidizing or oxygencontaining gas; the revivified catalyst has a restored activity and can be used again for the conversion of hydrocarbons.

The foregoing gives briefly the general conditions of preparation and of use of catalysts comprising dark or. black unglowed chromium oxide. However, not all solutions of chromic salts yield the desired dark-green hydrated chromium oxide on precipitation with an alkali. Many solutions yield a nongelatinou precipitate'such as a precipitate containing a high proportion of tion of a paraffin to light blue-green chromic hydroxide, which dries,

to a more or less chalk-like powder having little or no catalytic activity for the treatment or conversion of hydrocarbons. Still other solutions, of certain forms of chromic sulfate, may yield little or no precipitate on the addition of an alkali; however, on being boiled they generally do form a tate that on drying forms bluish chalk-like chromic oxide, which on drying has a low or negligible activity in the dehydrogenation, or hydrogenation, of hydrocarbons.

Although the reason for the differences in the behavior of various solutions of chromic salts upon the addition of an alkali is not clearly understood, a process has been disclosed in my aforementioned copending application Serial No. 113,091 (Patent No. 2,288,320) whereby the chromium is brought into such a condition that it does yield the desired dark-green hydrated gelatinous chromium oxide upon the addition of an alkali. In brief, this process comprises digesting nongelatinous or bluish chalky chromic hydroxide or oxide in a limited amount of an acidic aqueous solution, the acidity of the mixture being,

limited and theanions therein consisting predominantly of anions of a monobasic acid whose normal chromic salt is soluble in water and midrolyzes to give free acid; the digesting is continued until the chromium becomes capable of being precipitated as'dark-green gelatinous hydrated chromium oxide by an alkali in slight excess. After the chromium has been brought into the desired condition, it is precipitated and used for the preparation of a catalyst in accordance with the principles already discussed.

1 have now found that an improved catalytic material can be prepared by incorporating, in a new and novel manner, unglowed chromium oxide nongelatinous precipi-.

- preparation of such a catalyst its simplest form, the is effected by treating a concentrated aqueous solution of a chromic salt with less than a chemically equivalent amount of an alkali, intimately mixing with the resultant aqueous material a granular supporting material, and subsequently treating the resultant mixture with such an additional amount of alkali that the total amount of alkali used is equivalent to, or in slight excess of, the amount upon a porous support. In

chemically or stoichiometrically equivalent to the original chromic salt. The resultant (mixture of solid materials is freed from excess water and is washed to remove water-soluble material, and it is subsequently'dried and treated in accordance with procedures already discussed herein for preparing catalysts comprising chromium oxide. I prefer that the initial amount of alkali present should be between 25 and '75 per cent of the chemically equivalent amount of chromium figured as trivalent chromium, and preferably it should be between about 50 and '70 per cent of the equivalent amount.

I have further found that a preferred form of my improved catalytic material comprises dark unglowed chromium oxide incorporated upon a instead; for example,

support and prepared from a form of chromium oxide that normally does not form a catalytic material suitable for the conversion of hydrocarbons or the treatment of hydrocarbon'iractions. As disclosed in my copending application Serial No. 113,091 (Patent No. 2,288,320), of which this is a continuation-in-part, various chromic salts, when initially treated with an alkali, give a nongelatinous precipitate of chromium hydroxide or oxide that does not form a highly active catalyst for the treatment of hydrocarbons. As further disclosed in said copending application, such nongelatinous chromium oxide can be so treated in the presence of a limited amount of a monobasic acid that it is converted to a form that will produce a gelatinous hydrous chromium oxide precipitate upon the addition of a suitable amount of an alkali. This treatment may comprise adding to the nongelatinous precipitate a monobasic acid in an amount between 25 and 50 per cent of the amount chemically equivalent to the chromium oxide. Other procedures giving mixtures equivalent to the resulting mixture may be used chromic salt of a monobasic acid that upon the addition of alkali would form a nongelatinous precipitate, the treatment may comprise adding to a concentrated solution of the salt one-half, or slightly more, of the amount of an alkali that would be required to convert the chromic salt to chromic hydroxide. Further treatment of the resultant mixture by digesting it inaccordance with the procedure described in my aforementioned application (Patent No. 2,288,320) changes the chromium until it is in a form suitable for yielding a gelatinous precipitate. In preparing this preferred form of my improved catalytic material, I mix a granular support with the material resulting from this digesting part of the treatment of my previously disclosed process. which comprises adding a limitedamourpt of a monobasic acid to -a nongelatinous chromium oxide or adding a limited amount of an alkali to a chromic salt of a monobasic acid that would form a nongelatinous precipitate, and subsequent-, 1y I add an alkali in slight excess to fiect final precipitation of the chromium as dark-green gelatinous hydrated chromium oxide.

An object of the present invention is to proif the initial material is a the accompanying of an alkali in slight excess :tained, especially oxide catalysts, chromium vide a process for preparing comprising chromium oxide. Another object is lysts comprising unglowed chromium oxide.

Another object of my invention is to provide a process for the utilization of chrome compounds normally incapable of forming a darkgreen gelatinous precipitate upon addition or an alkali for the preparation of supported catalysts comprising dark or black ungiowed chromium oxide. 7 Other objects and advantages of the invention will be obvious to supported am disclosure.

In one specific embodiment, the invention comprises the process of transforming a chromic compound normally incapable gelatinous precipitat upon the simple addition capable of giving such a precipitate,-and incor porating the chromium -in the with a granular porous carrier, the chromium to provide supported catathose skilled in the art, from so that it becomes,

chromic compouii" ing a dark-green gelatinous precipitategoi hy-v drated chromiumoxide upon addition of an alkali. The procedure for this transformation varies somewhat for diii'erent initial chromic compounds, butin general it involves digesting nongelatinous chromic hydroxide or hydrous oxide in a limited amount of a concentrated acidic whose anions consist predomiwhose normal chromic salt distion is increased somewhat during the digesting,

of giving a dark-green" being in the form- 01 dark-green gelatinous hydrated chromium oxide obtained by an alkali in slight excess.

In this embodiment, the initial chromic compound may be any chromic compound that does not yield a dark-green gelatinous precipitate of hydrated chromium oxide upon addition 01' an alkali in slight excess. For example, it may be the light blue-green chalky precipitate of chromic hydroxide or hydrous oxide that at times isobif considerable sulfate is present, when a solution of an alkali is mixed with a solution of a chromic salt or with a solution reduction of the chromium in a hexavalent chromium compound, such as'a chromate or a dichromate, to the trivalent condiby precipitation mixture of acid and oxide becomes a colloidal solution or sol, and i1 quite tion. Such chromic oxide is generally somewhat hydrated and may vary considerably in color and physical characteristics, sometimes possessing the desirable dark-green color and/or the desirable gelatinous texture to a minor degree. Other suitable chromic compounds are those that yield such nongelatinous chromic oxide on addition of an alkali; sulfate and chromic chloride, violet chromic nitrate, and the like. Still other suitable chromic compounds are those that yield a precipitate only upon boiling'aiter the addition of an alkali. Also thick and viscous; this eral hours. Then a small sample of the resulting examples are certain forms of chromic to be included among suitable chromic compounds alkali, preferably ammonium hydroxide, from-a solution of a chromic salt or from a solution prepared by the well-known wet-method reduction of the chromium in a. hexavalent'chromium compound .to the trivalent condition. In some cases, standing for some hours, or heating or boiling for a more .or less prolonged period, sary -to aid the precipitation. 'The precipitate may be separated from the solution and may be washed to reduce the content of occludedsalts or ions; ifdesired, it mayhave been aged for days or weeks, but aging is not necessary.

Any such initial chromic compound is transformed or converted, according to theproc'ess of my invention, so that may be necesa mixture of chromic but the acidity need not exceed that present in oxide and one-half of the amount of such an acid that is chemically equivalent to the chromic oxide. The digesting temperature is preferably about 200 to 250 F.

In one specific embodiment of-the invention, bluish chalkychromic oxideisrtreated with about one-fourth as much of a monobasic acid as would be stoichiometrically required to convert all of the oxide to the corresponding normal chromic nitric, or trichloracetic' acid, is preferred, as its action is more rapid than that of a weaker acid, such as acetic or other monocarboxylic acid having up to four carbon atoms per molecule. The is triturated until it concentrated it will resemble a paint in appearance; the water content oi the mixture is preferpreierably digested at. about its boiling point while being vigorously stirred, until it becomes very digesting may require sevsol is diluted with wate yields a suitable dark-green gelatinous v precipitate uponbeing made alkaline.

If the original chromic compound is in the form of bright-green: chromic oxide, such as that in it becomes capable" of yieid- 75,

a valence greater than three, which acts as a dis solution catalyst; then chromic hydroxide or hydrous oxide is precipitated by the addition of an alkali, and the precipitate is treated in the manner already described. If a spentcatalyst is used moved, as by oxidation with air,.before the dissolution in hot concentrated sulfuric acid.

basic acid, an

and hydrolyzes to give free acid.

4 spending chromic salt may be used. Similarly, in the preparation of a mixed oxide catalyst, the acid maybe introduced in a state of chemical combination with one or more of the metallic elements of. the catalyst, such as a suitable salt 01' aluminum, zirconium and the like, among which is chromium, as in the form of one or more salts. Such'chromic or other salts of monobasic acids maybe considered to undergo hydrolysis in aqueous solution, liberating the free acid, and thus they are more or less equivalent to the acid itself. However, salts ,of metals that would impair the activity of thefinal catalyst should-be avoided.

A convenient way of obtaining the desired degree of acidity in a mixture to be digested is to add enough alkali, preferably ammonium hydroxide, to a concentrated solution comprising a chromic salt of a suitable monobasic acid to combine with'about half, or somewhat more, of the acid present in the chromic salt, whereby an incomplete rormation of hydrous chromium oxide is effected, and the residual chromic salt supplies the acid required for the digesting. The resulting mixture is then heated, whereby 'it is concentrated and digested in a manner similar to that just described. After such digesting is completed, the chromium is incorporated as dark-green gelatinous hydrated chromium oxide in a catalytic mixture that, upon drying and reducing, preferably in accordance with the aforementioned copending application of Morey and Frey (Patent No, 2,312,572) yields the desired catalyst.

Besides. the chromium oxide and any other desired catalytic, promoting, or stabiliing oxide or material, the-catalytic mixture comprises" a support or carrier whose chief function is to support the catalytic oxide or oxides but whose properties may include a catalytic-activity for the treatment of .hydrocarbons that is less pronounced than that of black uhglowed chromium oxide, or some promoting or. stabilizing characteristics. Thus, to a concentrated solution of chromic chloride, such as a solution that is approximately -ne molar or somewhat stronger, there is, added with stirring an amount of a conchtrated solution of an alkali, such as ammonium, sodium, or potassium hydroxide, equivalent to 50 to '75 percent of the chromic chloride, while the mixture is heated to asomewhat elevatedtemperature. To the resultant mixture is then added a porous granular supporting ma-: terial in an amount equal to aboutthree times the weight of the chromic oxide equivalent of the total chromium present. While this mixture is stirred, additional alkali is added to precipitate hydrous chromium oxide completely. manner the porous granular supporting material is thoroughly impregnated with, and subsequently coated'with, hydrous chromium oxide. The impregnated and coated support is washed with water and dried in air, and after reduction is quite active and rugged and highly eflicient for the formationof polymerizable oleflns from parafilnic hydrocarbon gases heavier than methane. V I

The support or carrier may, in general, be any granular porous material that is capable of withstanding elevated temperatures, up to about 1400" F., and the conditions present during revivification of the catalyst by an oxygen-containing gas at an elevated temperature. Particularly desirable are minerals-capable of withstanding dehydrogenation temperatures wlthout mechanical failure and possessing not only high specific sur-' In this 7 7 ever, 1

face and porosity but Supports having these also ready perviousness. characteristics are obtained from hydrous minerals, especially'hydrous crystalline minerals such as gypsum, gibbsite, or the like, by heating them to drive out combined water, so that a pervious skeletal structure of the mineral itself remains. Certain metamorphosed minerals, such as mica and its relatives and various clays having a somewhat stratified structure, such a bentonite and montmorillonite, may be used as supports; those having good porosity and perviousness may be readily selected by simple tests for these characteristics. Among suitable preferred carriers are alumina, bauxite, kieselguhr, magnesia,, silica gel, thoria, and zirconia. These supports are not to be considered as being complete equivalents of each other; they may or may not possess catalytic activity of their own. Of these materials, alumina and bauxite are preferred, especially hard bauxite, such as that found as pebbles in the region around Bauxite, Arkansas; such bauxite exhibits an exceptionally high resistance to abrasion and an exceptionally good catalytic activity for the treatment of hydrocarbons, and it is less expensive, all things being considered, than most of the other carriers mentioned. The carrier, in the form of granules of any desired size, is preferably heated before use to a temperature of about 1100 F., in order to expel volatile matter and to increase its porosity;

Extraneous soluble or finely divided'matter may be advantageously removed by washing with water, a preliminary chemical treatment, especially with a dilute alkali solution, is also advantageous. Incorporation or combination of the dark-green gelatinous hydrated chromium oxide and any associated oxides with the carrier may be effected in everal ways. A preferred-procedure comprises diluting the viscous sol obtained from such a digesting as dispersing the sol in several times its own volume of hot water; admixing the carrier granules: and precipitating the catalytic hydrous oxides in and upon the carrier granules, as by adding an alkali, advantageously a volatile alkali like ammonium hydroxide, in slight excess. Another procedure comprises diluting the sol with about one to three times its own volume of hot water; admixing enough carrier granules to absorb the resulting diluted sol; mixing the granules containing the absorbed sol with a solution of an alkali in slight excess, whereby dark-green gelatinous hydrated as with several times its own volume' of hot water;

precipitating dark-green gelatinous hydrated chromium oxide by the addition of an alkali, preferably ammonium hydroxide; washing the pre-' cipitate; and mixing the washed precipitate with carrier granules. Such a procedure does not, however, produce results equivalent to those produced by the procedure just described. Still other procedures, whichwill be obvious to those skilled in the art, may be used at various times. Howprefer to use one of the first-mentioned that already described, as bywill be obvious to those skilled in 2339349 procedures, wherein the granular support intimately mixed with procedure is followed. Although I am not sure asto the explanation for this superiority, be due to the combination of and impregnation of the carrier with, or

The carrier granules may be of size and shape;

any desired a size within the range of 4 to 20- admixing the carrier, in the form of small granules orof a powder, with the precipicatalyst. methods of obtaining composite granules, such as. pelleting,

the art.

5 mium oxide in the intimately with chromium oxide, as by tritura- 'tion. Thefirst mentioned procedure is preierred.

The details of drying and of reducing the chrosupported catalysts of the present invention preferably are substantially the same as those that are mentioned hereinbei'ore for chromium oxide gel catalysts and that are I also disclosed in the aforementioned copending application of Morey and Frey (Patent No. 2,312,572).

The following examples are given purely for the purpose of illustrating some of the many possible modes of practicing the invention; --they are not to be taken as limitations of the invention.

About 300 grams or so duced chr turated in about 400 cc. of concentrated hydrochloric acid until no lumps remain. The result- 1 ing mixture is stirred and digested at about its boiling point'for about an gelatinous consistency, the sol is diluted with several liters of hot water, and about a liter of preslight excess,. while that the precipitate the bauxite.

ed only slightly-in activity during 24 hours; and when finally taken out necessarily establishing a gas containing initially about 1 per cent of free oxygen. After this burning-out procedure and subsequent reduction with hydrogen it is again suitable for additional use.

Example II One moi, '400grams, of crystalline violet chromic nitrate is melted in its water of crystallization, and 140 cc. of 28 per cent aqua ammonia, which is sufiicient to react with about two-thirds of the chromium, is added slowly while the mixture is stirred and heated. On continued heating and evaporation of the mixture, the resulting light-blue chalky precipitate is dispersed into a sol that eventually becomes very thick and viscous. After about three hours of such heating, during which the temperature increases to about 250 F., a .test portion, diluted with hot water and treated with a slight excess of ammonium hydroxide, yields a dark-green gelatinous precipitate. The sol is diluted with about twice its own volume of hot water and, slowly poured into about a liter of dried alumina-gel granules, whichare agitated to ensure uniform distribution of the sol; the mixture is heated, if necessary, to drive off any excess water, so that all of the sol is absorbed by the granules. The granules are mixed with an excess of a dilute solution of ammonium hydroxide, whereupon dark-green gelatinous hydrated chromium oxide' is precipitated in the pores of the alumina granules. The granules are washed three times by decantation, and are dried, dehydrated, and reduced as in Example I. The catalyst thus produced has an excellent catalytic activity for the conversion of multicarbon paraflins into monoolefins and is rugged and longlived. It is also useful and rugged for the production, under dehydrogenating conditions, of dioleflns such as butadiene from monoolefins of the same number of carbon atoms per molecule.

Example III An aqueous solution having a concentration of approximately one mol'per liter is prepared from green chromic nitrate. To this solution is added,

with thorough stirring, suflicient sodium hydroxide to be equivalent to about per cent of the chromium, that is, a little over one and one-half mols'of sodium hydroxide is added for every mol of chromic nitra A thorough stirring of the solution is continued,

and three-fourths of an equal volume of granular, calcined magnesite, screened to 4 to 8-mesh, is slowly added. Agitation of the mixture is contlnued while additional sodium hydroxide is slowly added until a slight excess is present. The granules, which now are impregnated and coated with gelatinous chromium oxide, are washed and dried in air at a slowly increasing temperature to a final temperature of about 400 F. The catalyst is then reduced by treatment with hydrogen, and is highly eflicient and rugged for the treatment of a natural-gasoline fraction to increase its octane number, andfor the dehydrogenation of lower-boiling hydrocarbons.

Example IV Sodium dichromate is reduced with sugar in the presence of an excess of hydrochloric acid. Three-fourths of the resulting chromic chloride solution is diluted with hot water; and the chromium is precipitated by the addition of ammonia in slight excess. The resulting light blue-green comes a syrup. The syrup and the precipitate are mixed and triturated until a homogeneousappearing sol results. The mixture is digested at about 215 F., and at intervals, successive small amounts of concentrated hydrochloric acid are added until a test portion of the sol, when diluted and treated with ammonia in slight excess, yields a dark-green gelatinous precipitate. The sol is then diluted with hot water, and ammonia is added in slight excess to precipitate the chromium as dark-green gelatinous hydrated chromium oxide. The precipitate is washed three times by decantation, about three times its volume of granules of dehydrated bauxite. The coated bauxite is. dried, dehydrated, and reduced as in Example I. The resulting catalyst is rugged and long-lived when used to effect treatments of hydrocarbons.

Many modifications of the invention will be obvious to those skilled in the art. For example, the digesting may be efiected at increased temperatures in an autoclave, whereby the period of digesting is appreciably decreased. In view of the manypossible modifications, the invention should not be limited unduly by the foregoing specification and examples, but it should -be'understood to be as extensive in scope and equivalents, withinthe scope of asth'e prior art allows.

The practice of the invention results in the preparation of supported chromium oxide catalysts, which preferably comprise dark or black unglowed chromium oxide. It utilizes chromic compounds originally incapable of forming darkgreen gelatinous hydrated chromium oxide, for the preparation of such supported catalysts comprising black unglowed chromium oxide. These catalysts are highly eiiicient for the treatment and conversion of hydrocarbons and petroleum fractions, but they may also be used for other conversions in which they are effective.

I claim:

1. A process for preparing a chromium oxide catalyst, which comprises digesting a mixture comprising nongelatinous hydrous chromium oxide in a concentrated acidic aqueous medium whose anions consist substantially entirely of anions of a monobasic acid whosenormal chromic salt is soluble in water and hydrolyzes to give free acid, said mixture having an acidity not substantially greater than that present in a mixture of chromic oxide and onealf its chemical equivalent or said digesting being continuedfor such a period of time that a sol is obtained that is capable of I yielding a dark green and gelatinous precipitate on the subsequent addition or an alkali in slight excess, admixing therewith a porous granular supporting material, adding an alkali in slight excess to precipitate gelatinous hydrous chromium oxide, and washing and drying the refiltered, and mixed with the appended claims,

mixture comprising equal amounts of chromium in the form of chromic oxide and in the form of the chromic salt of said monobasic acid, and said digesting being continued for such a time that a viscous sol is obtained that is capable of yielding a dark-green gelatinous precipitate on addition of an alkali in slight excess, and incorporating the chromium in said sol with a granular porous carrier, the chromium being in the form of dark-green gelatinous hydrated 'chromium oxide obtained by precipitation by an alkali in slight excess.

3; A process for preparing a catalyst, which comprises digesting a mixture comprising nongelatinous hydrous chromic oxide and an acidic aqueous solution whose anions consist predominantly of the anions of a monobasic acid whose normal chromic salt dissolves in water and hydrolyzes togive free acid, said acidic solution being used in an amount not in excess of that required stoichiometrically to produce a mixture comprising equal amounts of chromium in the form of chromic oxide and in the form of the chromic salt of said monobasic acid, and said digesting being continued for such a time that a so] is obtained that is capable of yielding a darkgreen gelatinous precipitate on addition of an alkaliin slight excess, incorporating the chromium in said sol with a granular porous carrier, the chromium being inthe form of dark-green gelatinous hydrated chromium oxide obtained by precipitation by an alkali in slight excess, and drying and reducing the resulting supported chromium oxide catalyst. I

4. The process as defined in claim 3 and further characterized in that the chromium in said sol is incorporated with said carrier by diluting said sol, precipitating dark-green gelatinous hy drated chromium oxide from the diluted sol by the addition of a solution of said alkali, washing the precipitated chromium oxide, and mixing the washed chromium oxide with said granular carrier.

5. A process for preparing a catalyst, which comprises digesting a mixture comprising bluish chalky hydrous chromic oxide with a concentrated aqueous solution of a monobasic acid whose normal chromic salt dissolves in water and hydrolyzes to give free acid, the amount of aqueous solution being equivalent to approximately one-fourth that amount required stoichiometrically to convert all of the chromic oxide to the corresponding normal chromic salt, until the mixture becomes a viscous sol, adding from time to time additional small amounts of aqueous solution of the monobasic acid while continuing the digesting until a small test portion of the resultant sol, when diluted with hot water and treated with a solution of an alkali in slight excess, yields adark-green and gelatinous precipitate, the total amount of aqueous solution of the monobasic acid-that is used not exceeding one-half of that required stoichiometrically to convert all of the chromic oxide to normal chromic salt, incorporating the chromium in said sol with a granular porous carrier, the chromium being in the form of dark-green gelatinous hydrated chromium oxide obtained by precipitation by an alkali in slight excess, and drying and reducing the resulting supported chromium oxide.

6. A process for preparing a catalyst, which comprises digesting a mixture comprising bluish chalky hydrous chromic oxide and a concentrated aqueous solution of a chromic salt of a monobasic acid in an amount equivalent to approximately one-half as much chromiumas said chromic oxide, until the mixture becomes a viscous sol, adding from time to time additional small amounts of the chromic salt while continuing the digesting until a small test portion of the resultant sol, when diluted with hot water and treated with a solution of an alkali in slight excess, yields a dark-green gelatinous precipitate, the chromium in the total amount of chromic salt added not exceeding the total amount of chromium in said chromic oxide, incorporating the chromium in said sol with a granular porous carrier, the chromium being in the form of dark-green gelatinous hydrated chromium oxide obtained by precipitation by an alkali in slight excess, and drying and reducing the resulting supported chromium oxide.

'7. A process for the preparation of a supported chromium oxide gel catalyst, which comprises digesting a mixture comprising nongelatinous hydrous chromic oxide with an amount of hydrochloric acid that is equivalent stoichiometrically to from approximately 25 to approximately 50 per cent of the chromic oxide in the mixture, for such a period of time that the product obtained yields a dark-green and gelatinous precipitate of hy drous chromic oxide on the addition of alkali, admixing therewith a porous granular catalyst supporting material, adding an alkali in slight excess to precipitate gelatinous hydrous chromic oxide, and washing and drying the resultant impregnated and coated material.

8. A process for the preparation of a supported chromium oxide gel catalyst, which comprises digesting a mixture comprising nongelatinous hydrous chromic oxide with an amount of nitric acid that is equivalent stoichiometrically to from approximately 25 to approximately 50 per cent of the chromic oxide in the mixture, for such a period of time that the product obtained yields a dark-green and gelatinous precipitate of hydrous chromic oxide on the addition of alkali, admixing therewith a porous granular catalystsupporting material, adding an alkali in slight excess to precipitate gelatinous hydrous chromic oxide, and washing and drying the resultant impregnated and coated material.

9. A process for the preparation of a supported chromium oxide gel catalyst, which comprises adding to a concentrated aqueous solution of chromic nitrate an amount of an alkali which. is equivalent stoichiometrically to approximately two-thirds of the chromic nitrate, digesting the mixture for such a period of time that the prodnot obtained yields a dark-green and gelatinous precipitate of hydrous chromic oxide on the addi. tion of alkali, admixing therewith a porous gram ular catalyst support, adding an alkali in slight excess to precipitate gelatinous hydrous chromic oxide, and washing and drying the resultant impregnated and coated material.

- 10. A process for the preparation of a supported chromium oxide gel catalyst from a chromic compound that normally yields a substantially nongelatinous precipitate of hydrous chromium oxide when alkali is added to an aqueous solution thereof, which comprises adding to a concentrated aqueous solution containing such a chromic compound alkali to precipitate nongelatinous hydrous chromic oxide, segregating the precipitated chromic oxide and digesting it with from approximately 25 to approximately 50 per cent of its stoichiometrical equivalent of a monobasic acid whose chromic salt is soluble in water and steps which comprise digesting a mixture comprising nongelatinous hydrous chromic oxide and an acidic aqueous medium whose anions consist predominantly of the anions of a monobasic acid whose normal chromic salt dissolves in water and hydrolyzes to give free acid, said acidic solution being used in an amount not exceeding that required stoichiometrically to produce a-mixture comprising equal amounts of chromium in the form of chromic oxide and in the form of the chromic salt of said monobasic acid, and said di- 'gesting being continued for such a time that a sol is obtained that is capable of yielding a green gelatinous precipitate on the addition of an alkali in slight excess, admixing therewith a porous granular supporting material which consists predominantly of granulessmaller than about 20- mesh, subsequently adding an alkali in slight excess to precipitate green gelatinous chromium hydroxide;.washing and drying the resultant material in a manner such as to produce an im-' pregnated and coated granular material compriselasaaee ing predominantly granules larger than 20-mesh andeach containing a plurality of granules of said uppo ting material, and reducing the dried material in an atmosphere of a reducing gas. 12. A chromium oxide catalyst prepared by the steps which comprise digesting a mixture comprising nongelatinous hydrous chromium oxide and a concentrated acidic aqueous medium whose anions consist predominantly of the anions of a monobasic acid whose normal chromic salt dissolves in water and hydrolyzes to give free acid, said mixture having an acidity not substantially greater than that present in a mixture of chromic oxide and one-half its stoichiometric equivalent of such a monobasic acid, containin said digesting for such a period of time that a sol is obtained that is capable of yielding a green and gelatinous precipitate on the addition of an alkali in slight excess, diluting said sol with water, therewith? suiiicient granular supporting material to form a final catalyst com:- prising between 5 and 50 per cent chromium oxide, subsequently adding an alkali in slight excess 7 to precipitate gelatinous chromium oxide, washing the resultant impregnated and coated material, drying the washed material, and reducing the dried material in an atmosphere of a reducing gas at a temperature rising suuicientiy slowly within the range or about 300 to 570 F. that spontaneous thermal decomposition of chromium oxide is substantially avoided.

. GLEN H. MOREY.

Patent No. 559:54-9- CERTIFICATEOF CORRECTION. o

' January 18, 194k.

GLEN H. money. It is hereby certified that error arpears in the printed specification of the above numbered patent requiring correction as foliows: Pagefl, sec- 0nd column, linel5, claim 12', for "containing" read "continuingraud that the eaid Letters Patent should be read with this correction therein that thesame may conform to the record of the case in the Patent Office,

Signed and sealed-this 18th dey of April, A. D. 19141;.

gr Leslie Frazer fiscal)" Acting Commissioner of Patents. 

